[ty] Print salsa memory usage totals in mypy primer CI runs (#18973)

## Summary

Print the [new salsa memory usage
dumps](https://github.com/astral-sh/ruff/pull/18928) in mypy primer CI
runs to help us catch memory regressions. The numbers are rounded to the
nearest power of 1.1 (about a 5% threshold between buckets) to avoid overly sensitive diffs.

.github/workflows/mypy_primer.yaml

@@ -48,6 +48,8 @@ jobs:
 
       - name: Run mypy_primer
         shell: bash
+        env:
+          TY_MEMORY_REPORT: mypy_primer
         run: |
           cd ruff